The present invention relates to a computer system, and, more particularly, to a computer system like a personal computer, which has a resume function called a hibernation system.
The entire contents of Japanese Patent Application No. 8-247798 filed on Sep. 19, 1996 are incorporated herein by reference.
Conventional portable personal computers, particularly, those operable by battery power, are equipped with a resume function which saves information about the display status and the operational status of the system and/or the operational status of an application program in a backed-up memory before actually being powered off when a power switch is set off, and restores the saved information, upon power on, to resume the system from the status before the power-off time. According to the resume function (or suspend/resume function), information stored in the main memory, and status information or the like set in the internal register of a CPU (Central Processing Unit) are saved, and when the computer is powered on next, those information are restored.
A rechargeable battery and an auxiliary battery are used as a backup power supply needed for the resume function. When a user forgets to exchange such an auxiliary battery with one having sufficient power or the remaining battery capacity (currently usable power capacity) is insufficient, however, the execution of the resume function may result in erasure of information (memory contents) to be saved in the memory. To cope with this shortcoming, a hibernation type resume function has been developed which saves the memory contents on a hard disk drive (HDD) installed in the system at the time the resume function is executed, so that it can protect the memory contents even when power supply to the system is completely stopped.
Since compact and large-capacity HDDs are recently installed in portable personal computers or so-called notebook type computers, the hibernation type resume function which saves information about the operational status of the system and/or the operational status of an application program on such an HDD is effective. HDDs are one kind of non-volatile memory means capable of saving data without requiring backup power and can ensure the resume function almost permanently.
Because the hibernation type resume function can save the memory contents, which have been saved at the power-off time, on an HDD, one kind of non-volatile memory means, that requires no backup power, it is possible to prevent the memory contents from being unintentionally erased and to reliably resume the system from the state before the power-off time when the system is powered on again.
The hibernation type resume function however has the following shortcoming. As HDDs suffer slower access speeds than IC memories or the like, they require a certain time in the disk access operation for writing the memory contents on a disk or reading the memory contents therefrom. When the memory contents are saved on an HDD by the resume function (suspend process) as the power switch is set off and the power switch is set on immediately to resume the operation, particularly, it takes a considerable amount of time to restore the saved memory contents into the original memory from the HDD. When this hibernation type resume function is adapted to a portable personal computer like a notebook type, therefore, the user's operability is degraded.
As a solution to this problem, a so-called standby control function (a standby mode) has been developed which keeps supplying backup power to the memory only for a predetermined period of time even when the power switch is set off so that when the power switch is set on again within the predetermined time, the memory contents can be restored quickly from the memory to set the system in the operational condition. In other words, when a predetermined time passes, the standby control function is released to power off the system immediately. When used in a notebook type personal computer which operates on battery power, therefore, this system is effective because it can reduce the consumed power of the battery. Unlike battery-driven type, however, personal computers which can use AC adapters to utilize commercially available AC power (hereinafter called AC power) as system power do not require a reduction in consumed power so much. For such personal computers, it is more important to improve the users' operability.